Researchers have proved that people can be conditioned with behaviors in their sleep — and then exhibit those same behaviors when they're awake, without any memory of the earlier training. While there's some suggestion this could lead to methods of learning information in your sleep, the potential for night-time conditioning is pretty scary.

A new paper published in Nature Neuroscience shows that people can be conditioned to respond to a particular sound, via the use of smells. And the research tells us a lot about how your brain learns when you're asleep and dreaming.

In the experiment, which was conducted by Noam Sobel, Anat Arzi, and Ilana Hairston at the Weizmann Institute in Tel Aviv, volunteers were sprayed with both pleasant and unpleasant odors while they were fast asleep. And like people who are wide awake, the volunteers reacted by taking either weaker breaths (like short sniffing) when the smell was nasty, and stronger, longer breaths when it was nice.

At the same time that the smells were being administered, the researchers matched each smell with a very specific tone. They performed the experiment repeatedly and long enough to provoke a Pavlovian response in the volunteers such that, while they were still sleeping, they could either elicit the shallow or deep breath response by simply playing the sound associated with either the pleasant or unpleasant odor.

Now here's where the experiment gets interesting — not that it hasn't been a riveting tale up to this point: The researchers then played the distinctive tones to the volunteers while they were awake. What they found was that each tone that had been matched to either a pleasant or unpleasant smell would cause the volunteer to take either a deep or shallow breath depending on which smell the sounds were associated with.

In other words, they had learned a completely new response — albeit a conditioned one — while they were asleep. The lesson of the smells remained with them even while awake. And it's worth noting that the volunteers had no conscious recollection of the experiment.

Further experiments revealed that the best learning happened during the REM phase of sleep (which surprised the researchers), but it could only be transferred to waking memory when it was conducted during the non-REM phase of sleep.

What this research suggests is that people can actually have their conscious behavior modified during sleep. In terms of next steps, the researchers are hoping to explore the limits of this kind of learning — such as what sort of information you can actually learn during sleep.